Atomic and molecular beam scattering from macroscopically rough surfaces

Abstract

The scattering of thermal energy atomic and molecular beams from macroscopically rough surfaces has been found to display scattered flux distributions that are typically skewed towards the incoming, beam i.e., backscattered. Such an observation is consistent with the results reported in the literature describing flow-conductance measurements, which are less than the conductance calculated assuming the Knudsen (diffuse) scattering law. Two types of surfaces were studied in the present work: shot-blasted surfaces and gold-blacked surfaces. Both these surfaces displayed scattered flux distributions of a backscattered nature with only subtle differences noted between the two. The conditions required for backscattering are contrasted with the conditions which appear to be necessary for Knudsen scattering and the possibilities are considered for direct application of these observations to a description of the environment existent in typical vacuum systems.